The present invention relates to a multi-piece solid golf ball. More particularly, it relates to a multi-piece solid golf ball having very soft and good shot feel, and excellent rebound characteristics and flight performance, when hit by golfers who swing a golf club at low head speed.
Golf balls, which are commercially selling, are typically classified into solid golf balls such as two-piece golf ball and three-piece golf ball, and thread wound golf balls. Recently, in the solid golf balls, flight distance can be improved while maintaining soft and good shot feel as good as a conventional thread wound golf ball. Therefore the solid golf balls occupy the greater part of the golf ball market. A multi-piece golf ball, which is represented by a three-piece golf ball, has good shot feel while maintaining excellent flight performance, because of accomplishing various hardness distributions as compared with the two-piece golf ball (Japanese Patent Kokoku publication No. 48473/1992, Japanese Patent Kokai publication Nos. 24084/1995, 322948/1997, 216271/1998 and 151320/1999).
Three-piece solid golf balls comprising a two-piece core, which are formed by placing an intermediate layer between the core and the cover of the two-piece solid golf ball, are suggested in Japanese Patent Kokai publication Nos. 322948/1997, 216271/1998 and 151320/1999. The intermediate layer is formed from vulcanized rubber material having the same composition as the core of the two-piece solid golf ball. These golf balls are characterized by controlling the thickness of the intermediate layer to not less than 1.5 mm, which is relatively thick, and the intermediate layer is softer than the inner core. Therefore the rebound characteristics are largely degraded, which reduces the flight distance when hit particularly by golfers who swing the golf club at low head speed.
Three-piece solid golf balls, of which the intermediate layer is formed from thermoplastic resin, are suggested in Japanese Patent Kokai publication No. 24084/1995, Japanese Patent Kokoku publication No. 48473/1992 and the like. In the golf ball described in Japanese Patent Kokai publication No. 24084/1995, of which the intermediate layer is softer than the inner core, it is restrained to degrade the rebound characteristics when compared with the three-piece solid golf ball having soft type intermediate layer formed from the above vulcanized rubber. However, since the deformation amount at a portion nearby the surface of the golf ball is large, the shot feel when hit by golfers who swing the golf club at high head speed is heavy and poor. In the golf ball described in Japanese Patent Kokoku publication No. 48473/1992, since the hardness of the inner core is not adjusted to a proper range, sufficient flight distance and shot feel are not obtained.
In order to solve the problem, for example in Japanese Patent Kokai publication No. 226151/1999, a multi-piece golf ball (comprising at least one layer of cover), of which the intermediate layer is formed from vulcanized rubber and is harder than the inner core, is suggested. However, in the golf ball, the intermediate layer is hard, the shot feel is hard and poor.
There has been no golf ball, which has both excellent flight performance and good shot feel. It is required to provide a multi-piece golf ball having better shot feel and better flight performance.
A main object of the present invention is to provide a multi-piece solid golf ball having soft and good shot feel, and having excellent rebound characteristics and flight performance, when hit by golfers who swing a golf club at low head speed.
According to the present invention, the object described above has been accomplished by adjusting the deformation amount and hardness distribution of the core having multi-layered structure, the hardness and thickness of the outer core, the hardness of the cover to a specified range, thereby providing a multi-piece solid golf ball having soft and good shot feel, and having excellent rebound characteristics and flight performance, when hit by golfers who swing a golf club at low head speed.